1. Field of the Invention
The invention relates to a sensing circuit and a sensing method thereof, and more particularly, to a capacitance sensing circuit and a capacitance sensing method thereof.
2. Description of Related Art
In this information era, reliance on electronic products is increasing day by day. The electronic products including notebook computers, mobile phones, personal digital assistants (PDAs), digital walkmans, and so on are indispensable in our daily lives. Each of the aforesaid electronic products has an input interface for a user to input his or her command, such that an internal system of each of the electronic product spontaneously runs the command. At this current stage, the most common input interface includes a keyboard and a mouse.
From the user's aspect, it is sometimes rather inconvenient to use the conventional input interface including the keyboard and the mouse. Manufacturers aiming to resolve said issue thus start to equip the electronic products with touch input interfaces, e.g. touch pads or touch panels, so as to replace the conditional keyboards and mice. At present, the users' commands are frequently given to the electronic products by physical contact or sensing relationship between users' fingers or styluses and the touch input interfaces. For instance, a capacitive touch input interface characterized by a multi-touch function is more user-friendly than the conventional input interface and thus gradually becomes more and more popular.
However, given that a one-end sensing circuit is applied to the capacitive touch input interface, voltage of a capacitor under test is required to be measured and stored as a base line voltage before touch sensing with the capacitor under test, as shown in FIG. 1.
FIG. 1 shows the schematic waveforms of voltage of the capacitor under test before and after touch sensing. Before touch sensing, the one-end sensing circuit requires storing voltage V of the capacitor under test as a base line voltage. Next, a voltage variation ΔV of the capacitor under test can be obtained by subtracting the voltage V′ which is actually sensed by the capacitor under test from the base line voltage. Herein, the one-end sensing circuit stores the voltage variation ΔV in an internal capacitor therein by single edge couple. For instance, in FIG. 1, the one-end sensing circuit stores the voltage variation ΔV of positive edge couple of the waveforms in the internal capacitor therein.
Furthermore, the reference capacitance of the capacitor under test of the one-end sensing circuit is a fixed value, and therefore the external noise can not be canceled indeed, such that signal-to-noise ratio (SNR) of the one-end sensing circuit can not be enhanced effectively.